1. Field
The disclosed subject matter relates generally to formulations of collector compositions for the recovery of value minerals from mineral ore bodies. More particularly, the disclosed subject matter relates to organic sulfur-containing collector compositions and methods for using the same.
2. State of the Art
Froth flotation is a widely used process for beneficiating ores containing valuable minerals, often referred to as “value minerals”. Value mineral(s) refer to the metal, metals, mineral or minerals that are the primary object of the flotation process, i.e., the metals and minerals from which it is desirable to remove impurities.
A typical froth flotation process involves intermixing an aqueous slurry that contains finely ground ore particles with a frothing or foaming agent to produce a froth. Ore particles that contain the value mineral(s) are preferentially attracted to the froth because of an affinity between the froth and the exposed mineral on the surfaces of the ore particles. The value minerals are then collected by separating them from the froth. Chemical reagents, referred to as “collectors,” are commonly added to the froth flotation process to effect the separation. Certain theory and practice indicates that success of a flotation process for base metal sulfide and precious metal ores is dependent on the collectors which impart selective hydrophobicity to the value mineral separated from other minerals. See, e.g., U.S. Pat. No. 4,584,097, the entirety of which is incorporated by reference herein.
Other reagents, such as “frothers”, may be added to the process to provide a suitable basic froth phase to capture hydrophobic value minerals and facilitate separation and recovery thereof. Certain other reagents, referred to as “modifiers”, may be used to enhance separation and recovery of the desired minerals and/or metals. Modifiers, which can include pH regulators, may be used to modify and control the pH of the ore pulp in order to enhance separation and recovery of the desired minerals and/or metals. In some instances, compounds referred to as “activators”, such as copper sulfate, may be used to activate a certain value sulfide mineral in order to enhance collector coating on this sulfide mineral.
Froth flotation is especially useful for separating finely ground value minerals from the associate gangue or for separating value minerals from one another. Because of the large scale on which mining operations are typically conducted, and the large difference in value between the desired minerals and the associated gangue, even relatively small increases in separation efficiency provide substantial gains in productivity. Additionally, the large quantities of chemicals used in mining and mineral processing pose a significant challenge in terms of health and safety to humans and the environment. Consequently, the industry is continually searching for effective alternatives that increase safety while lessening the impact on the environment.
Currently, a large variety of organic sulfur-containing compounds such as xanthates, dithiophosphates, dithiocarbamates, etc, are utilized as collectors in the flotation recovery of value minerals from sulfide and precious metal ores. Existing thought about such compounds is that either the free acid or any salt of the acid can be used in flotation, and that all the salts and free acid are equivalent. In other words, it is believed that a sodium salt of an organic sulfur-containing acid can be substituted with a calcium salt or an inorganic ammonium salt, and obtain substantially the same result. Moreover, most of the collectors based on organic sulfur-containing salts are aqueous and are the sodium or potassium salts of sulfur-containing acid. Thus, when names of collectors are mentioned, such as a xanthate or dithiophosphate, it is in reference to a sodium, inorganic ammonium or potassium salt.
A commonly used collector, xanthic acid, is an ionic compound that is produced and transported as solid sodium or potassium salts of xanthic acid, widely known as xanthates, and is used as aqueous solutions at the mine site. While they have shown value in mining processes, xanthates oxidize and hydrolyze in the presence of water thereby releasing hazardous byproducts. Solid xanthate can pose a fire hazard. Other common water-soluble ionic collectors pose similar hazards to a varying degree.
Frequently it is advantageous to mix two or more collectors for use in a froth flotation process. These mixtures can either be two or more aqueous ionic collectors, or mixtures of ionic collectors with charge neutral oily collectors (referred herein as “neutral collectors”). The latter mixtures are often preferred because of certain characteristics. However, formulations of aqueous ionic collectors and non-aqueous neutral collectors in general present a significant challenge, as these formulations are often incompatible, unstable and generate toxic by-products, such as gases or aqueous species or precipitates, thus posing significant environmental and health hazards. These formulations are also physically unstable, i.e., they separate into phases and generate precipitates, thus minimizing the types of compositions that can be made using combinations of aqueous ionic collectors and non-aqueous neutral collectors and thereby negating or minimizing synergistic advantages. In fact, some aqueous collectors cannot be mixed with neutral collectors at all, e.g., xanthates, since they will result in chemically unstable compounds that generate toxic byproducts. Similarly, some neutral collectors cannot be mixed with aqueous collectors at all, e.g., dialkyl xanthogen formates.
Many formulations that contain either two or more ionic collectors, or mixtures of ionic collectors with charge neutral collectors, further utilize diluents and coupling agents to ensure compatibility. Such diluents and coupling agents may be hazardous. Indeed, in a few cases, compatible formulations cannot be prepared without significant dilution and/or introduction of undesirable coupling agents; even then, only a narrow range of formulations is practicable. The presence of water in these formulations can cause undesirable side reactions, generate species that are toxic and hazardous, and present a challenge to shipment of the same.
Many current collector formulations do contain water, which reduces the available active collector and contributes significantly to transportation costs. Given the recent increase in fuel costs, cost-effective transportation and energy savings are important in developing alternatives to current collectors.
In view of the foregoing, there is a need in the art to develop a stable collector formulation that offers cost savings as well as reductions in hazards to humans and the environment. The inventors of the instant invention believe the subject matter disclosed and claimed herein is an answer to those needs.